A method is presented for calculating the effects of steady energy and momentum sources on atmospheric wave propagation. This involves evaluating the weak feedback produced by the modulation of the source field by small-amplitude waves. Although the sources may, in practice, depend on a number of the wave field parameters it is only necessary to formally treat the fluid density modulation. This constitutes a generalization of Rayleigh's instability criterion for the generation of sound in heated air. The approach is applied to the propagation of internal gravity waves in a Boussinesq approximation and to high-frequency acoustic waves. In particular, a number of effects associated with the propagation of atmospheric waves through regions of convecting plasma are treated. These cases are relevant to the propagation of internal gravity waves in the F region of the high-latitude ionosphere. Some new theoretical results concerning the damping and stability of internal gravity waves in rapidly flowing plasma and under conditions of critical coupling between plasma flow and phase propagation are presented. ¿ American Geophysical Union 1993